GetGroupDataReader() failed when opening a group

we have a custom group with conditions in a custom view. Group was working fine for all users.Now one user is crashing his web-client when he tries to open this group. No error message appears, the browser is frozen and has to be closed. The other users can still use this group.

In event viewer is the following error: GetGroupDataReader() failed.And a sql query. The query seems to be right. Copy & paste the query to management studio returns no errors.

What we tried: VFS Application User Folder deleted,local cache deletedtried on different computers,tried with different browers (IE, Firefox)copied the group,recreated the group in lan client (group is working on lan)